1. Field of the Invention
The present invention relates to a steering control device of a vehicle properly performing a steering control in a straight-traveling braking state and in a straight-traveling acceleration state by independently steering left wheels and right wheels.
2. Description of the Related Art
Recently, with respect to a vehicle, a steering control device having various structures which can independently steer the left wheels and the right wheels (a steering control device which includes a steer-by-wire mechanism or a steering control device which includes a variable toe angle mechanism) has been developed and put into practice.
For example, Japanese Patent Unexamined Application JP-A-2004-268858 discloses a steering control system which includes a steering mechanism for independently steering left and right steering wheels and a unit for detecting lateral slide angles of the wheels, and independently controls the left and right steering wheels such that a cornering force becomes optimum for the respective left and right wheels in response to the lateral slide angles of the steering wheels so as to increase a gripping force during cornering of the vehicle.
However, in the above-mentioned system, the lateral slide angle at the center of gravity of a vehicle body is obtained based on a two-wheel model of a vehicle, a vehicle-body lateral slide angle is obtained at respective steering wheel steered positions based on the lateral slide angle at the center of gravity of the vehicle body, and the lateral slide angle of the steering wheel is obtained based on the vehicle-body lateral steering angle of the vehicle at the steering wheel steered positions. Further, the control is performed in response to the lateral slide angle of the steering wheel and hence, there exists a possibility that the responsiveness of the control is not favorable and many errors occur in the control. Further, in this system, both wheels are independently controlled in response to the cornering. Accordingly, when both wheels are controlled in a straight-traveling deceleration state or in a straight-traveling acceleration state, a braking distance is enlarged and, further, the acceleration performance can not be obtained efficiently.